In manufacturing a semiconductor device, an Al (aluminium) reflow process provides metal with excellent step coverage for filling high aspect ratio contact openings. In performing Al reflow on a semiconductor wafer, argon (Ar) gas can be blown on the back side of the wafer to improve temperature uniformity and thermal conductivity. However, the argon gas flow can separate the wafer from a heater table on which the wafer sits for the Al reflow by creating a pressure difference between a high vacuum chamber and the backside of the wafer. Thus, a clamp is used for preventing the wafer separation.
FIG. 6 illustrates a known clamp 100, which holds a semiconductor wafer during Al reflow. Clamp 100 includes a cap 102, a pad 104 and a mounting plate 106 which are made of stainless steel. Cap 102 and pad 104 are fixed to mounting plate 106 by screws 110. Clamp 100 can damage a semiconductor wafer that is fixed between pad 104 and mounting plate 106. For example, a wafer edge section that contacts the pad 104 may crack when heating causes clamp 100 and the wafer to expand. Although slots 108 are made in clamp 100 to suppress expansion of pad 104 that may contact and damage the wafer, the expansion can still damage the wafer during an actual process. Additionally, the surface of pad 104 can become rough, due to deformation of pad 104 during multiple high temperature processes. As a result, the rough surface of pad 104 can damage a surface of the wafer.